1. Field of the Invention
The present invention relates to an electronic control type automatic speed (gear ratio) changer, which is particularly effective in initiating reverse movement (backing) on a low coefficient of friction road surface liable to cause slippage, such as a snowy or frozen surface.
2. Prior Art
Heretofore, in a vehicle having an automatic speed changer, with the car speed at zero, that is, when the vehicle is stopped, the forward speed range has been set in such a manner as to always advance from first speed (first gear). Therefore, although there is no special problem in the case of normal running, on a low coefficient of friction road surface such as a snowy or frozen road, a vehicle so equipped was susceptible to wheel spinning which made initiation of advancement difficult.
With the advent of electronic control type automatic speed changers it became possible to freely regulate speed changing by electrically controlling a shift solenoid with a mode selection switch to provide a winter mode, a hold mode, etc., in order to prevent slippage on a road covered by snow or ice and to allow initiation of advancement in second or third speed.
However, with the above-described conventional technology, although initiation of advancement on a low .mu. surface as snow or ice could be suitably controlled, there was only one gear range, and the prevention of slippage was not possible.
Accordingly, the object of the present invention is to provide electronically controlled automatic transmission having the capability of providing a smooth reverse start under the above-described problematic conditions.